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Old 05-23-2018, 09:46 AM   #1
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Join Date: May 2018
Location: Seattle
Posts: 18
Engine Running Very Rough After P1128 & P1130 Codes

1999 Boxster 2.5L
71,xxx miles

I am looking for some feedback on the source of my woes. Currently the engine is running very rough at idle when cold and is not drivable. When blipping the throttle the engine will bog down. Letting the engine idle for 10 minutes or so it runs better and engine responds when blipping the throttle. I have not tried to drive it yet after warming up.

The Story………

The other day on the freeway I got a check engine light. The codes were P1128 & P1130. I didn’t record the freeze frame data, but it very similiar to the numbers listed below for the second occurrence. The car was running fine. I cleaned the MAF sensor and cleared the codes.

The next day I drove it to work and on some errands with no issues. Approx 80 miles with a mix of highway and city.

The second day I drove it. On the way home from work on the freeway I got the check engine light again. The same P1128 & P1130 codes were present. Car was running fine. The following freeze frame data was on my basic code reader.

Load 8.6%
FuelSYS1: CL
FuelSYS2: CL
Short fuel trim 1: 2.3%
Short fuel trim 2: 4.7%
Long fuel trim 1: 29.7%
Long fuel trim 2: 28.1%
RPM: 3022

The car was still running well. Figuring it wasn’t a big deal, I parked it for a few hours and cleared the codes. After clearing the codes I move the car out of the driveway I thought it was running a bit rough, but I thought maybe I am just being over sensitive.

The next morning, I fire up the car to go to work and it doesn’t run worth a crap. Since one of the systems of the P1128 & P1130 codes is an air leak I go and check the oil filler cap. When I took it off the car quit running.


Searching the various Boxster forums the common causes for the P1128 & P1130 codes are as follows.

Air intake leaking.
Fuel Pressure to low.
Fuel injectors contaminated.
Fuel supply volume to low.

A bunch of people have cleaned their MAF sensors with success. No luck for me. I feel the rough running engine may be symptom of something a bit bigger. I believe I have the original MAF sensor.

I put a bottle of fuel injector cleaner in, but I probably only burned 1 to 2 gallons before the engine troubles got worse.

I am leaning towards an air leak issue based on how the engine is running. I sprayed all the throttle body to intake connections and all associated vacuum lines I could find with carb cleaner. No change to engine RPM.

I took the hose that runs from the AOS to the throttle body off. I found fresh only in the line at both ends. Maybe about a teaspoon at the intake end. I haven’t had any of the standard AOS failing conditions. No clouds of white smoke at start up. The oil cap comes off easy while the engine is running. There is a slight vacuum at the filler. I believe this is the original AOS.

I have ordered a smoke generator so I can better trouble shoot any potential air leaks.


I am leaning towards the AOS as being bad. The fresh oil in the line, age of the AOS, poor engine running when cold. The fact that it runs better when hot I think is indicative of air leak sealing as it warms up.

What I am struggling with is, can a failing AOS generate the air leak type symptoms I am seeing?

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